The Duke Center for Learning Health Care (CLHC) proposes to host a single day workshop (Think Tank) that convenes national experts, thought leaders, and stakeholders to discuss issues related to the core data elements needed for comparative effectiveness research in oncology along with the definitions and ontology thereof. Insights from a recent Agency for Healthcare Research and Quality (AHRQ)-funded project at Duke and the University of North Carolina will be used as the foundation for this workshop. Consensus on the context, scope, and relationships of these elements will be agreed upon when possible, and an agenda for future development will be agreed upon where needed.